1. Field of the Disclosure
The present disclosure relates generally to fasteners for assembly of two or more panels of a workpiece, and more particular to a blind fastener having an installed flushness that requires little, if any, post-installation shaving or filling.
2. Description of the Background
Exterior airframe joints are required to be flush to reduce aerodynamic drag. It is therefore desirable to prevent any portion of a mechanical fastener from protruding beyond a surface of an outer panel of a workpiece in which the fastener is installed. It is also preferred to prevent any portion of a fastener from being recessed within the workpiece or recessed as compared to the remainder of the fastener. Having all portions of the fastener and the surface of the outer panel of the workpiece in an even plane is referred to as the “flushness” of the fastener. It is further desired to minimize the visibility of mechanical fasteners on an aircraft's exterior in order to improve appearance. Such flushness and appearance goals are easily met with conventional fasteners such as solid rivets, lock bolts, and threaded pins with nuts. Many pull-type blind fasteners also exhibit acceptable installed flushness. However, threaded blind bolts have always suffered from the need to have a corebolt break-off location vary by as much as 0.103 inch so that, in some grip conditions, the corebolt either protrudes above the surface of the outer panel by this amount or, if the break-off location is positioned to never break above the exposed body head surface, the corebolt breaks low, thereby leaving a cavity up to 0.103 inch deep. In either case, the fastener oftentimes requires milling of the protruding corebolt or filling (potting) of the cavity to produce the desired level of aerodynamic flushness.
A need therefore exists for a threaded blind fastener that produces a predictable and consistent flush installation throughout the gripping range and that minimizes the need for post-installation milling or potting.